The present invention relates to a lighting panel for a display such as liquid crystal display (LCD) for illuminating the display from the underside thereof as a back light.
FIG. 10 is a plan view showing a conventional lighting panel, and FIG. 11 is a sectional view taken along a line XIxe2x80x94XI of FIG. 10.
The lighting panel 12 made of a transparent plastic has a rectangular shape in plan view and an incident surface 12a by beveling a corner. An edge light 11 of an LED is provided corresponding to the corner 12a. On the underside of the lighting panel 12, a plurality of prisms 12b are formed as reflector members. The prisms 12b are concentrically formed with the light discharge point of the edge light 11 as shown in FIG. 11. The prism 12b has a vertical angle of 90 degrees.
The light emitted from the edge light 11 enters the lighting panel 12. The light in the lighting panel 12 is reflected by the prisms 12b and discharged from a discharge surface 12c. The discharged light enters a diffusion sheet 13 and discharges from the diffusion sheet to be applied to an LCD (not shown) in diffused rays.
Light discharged from the underside of the lighting panel 12 is reflected by a reflector sheet 14 to be returned to the lighting panel 12.
In such a device, the intensity of light becomes reduced toward the end distant from the edge light 11. Therefore, the LCD is not uniformly illuminated.
Furthermore, since the intensity of light in an area near the edge light is very high, prisms 12b must be arranged at high density, which causes the manufacturing cost to be increased and quality of the lighting panel 12 to reduce.
An object of the present invention is to provide a lighting panel which may be easily manufactured with simple arrangement of prisms.
According to the present invention, there is provided a panel for lighting a display comprising a lighting panel made of a transparent plastic and having rectangular both surfaces one of which is a reflection surface and the other is a discharge surface, an incident surface formed by beveling one of corners of the lighting panel, an edge light provided corresponding to the incident surface, a plurality of prisms circularly formed on the reflection surface of the lighting panel, edge lines of the prisms being concentrically arranged with the edge light at a predetermined interval, each of the prisms having a vertical angle xcex8 comprising a first inclination angle xcex81 on the edge light side and a second inclination angle xcex82 opposite to the first inclination angle xcex81, wherein there is a following relationship between the first inclination angle xcex81 and the second inclination angle xcex82,
xcex81(=89.5xc2x0xcx9c60xc2x0) greater than xcex82. 
The panel further comprises a prism sheet disposed corresponding to the discharge surface of the lighting panel, the prism sheet having a plurality of prisms on a surface corresponding to the discharge surface.
The prism has a circular edge line.
In another aspect, the prism is a circular lenticular lens.
These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.